EYE COLOR IN DROSOPHILA MELANOGASTER 



361 



its dominance, its known position in the suspected region, and 

 from its easy classification in the same flies with cream III, it 

 being a wing and bristle character. The double crossover result 

 (table 19) showed that cream III is situated to the left of dichaete. 

 The cream III dichaete crossover value (4.2) is considerably 

 smaller than the sepia dichaete crossover value (14.8) found in 

 heterozygous Cm experiments, so that cream III is known to be 

 between sepia and dichaete. The normal amount of crossing 

 over between sepia and dichaete is 11.0 so that the probable 

 position of cream III is 3.1 to the left of dichaete or 7.9 to the 

 right of sepia which is the zero position. 



TABLE 19 



The B. C. offspring from the outcross of a cream III ebony female to a dichaete male, 

 and the Fi dichaete females backcrossed singly to cream III ebony males 



The occurrence of the linkage variation and its testing had 

 diverted me from making tests of the effect of the cream III gene 

 in the absence of eosin as a base. Accordingly, the preceding 

 experiment was repeated, but in such a fashion that half of the 

 flies should be not-eosin. A cream III ebony female from the 

 high value stock was outcrossed to a simple dichaete male. 



Several of the dichaete daughters ( 



CrHi + e C, 



^) were back 



+ D'+ + 



crossed singly to cream III ebony males of the high stock. 

 The result (table 19, left side) showed that the gene responsible 

 for the dilution of eosin to the cream color gave by itself a color 

 somewhat similar to purple, that is, a 'magenta.' But when 



